Many conventional implementations of data processing systems require that such systems operate with a high level of integrity. As an example, a data processing system such as a computer-based vehicle navigation, operation or control system must operate with a sufficient level of integrity and accuracy such that the designers and operators of such a system can trust the system to perform properly in order to avoid hazardous conditions (e.g., the production of hazardously misleading information) which may endanger human life or property. Due to the complexity of modem day computerized data processing systems such as signal-based vehicle navigation systems, performing a verification process to determine that such systems operate at a required level or threshold of integrity can be problematic for system designers.
As an example, consider a conventional data processing system such as a Global Positioning System (GPS) that vehicles or individuals might use for navigation purposes. Generally, a GPS system includes a constellation (e.g. twenty-four or more) of GPS satellite space vehicles that orbit the earth. Each GPS satellite continually transmits, from space, specially coded GPS satellite signals (i.e., radio signals) that GPS receiver devices in vehicles or carried by individuals can receive and process. According to a specific orbital arrangement of the GPS satellites around the earth, a GPS receiver device positioned in the air or on the surface of the earth is provided with between five and eight different visible (i.e., receivable) GPS satellite signals from respective orbiting GPS satellites. By receiving and processing GPS satellite signals from four or more GPS satellites according to certain GPS navigation algorithms (e.g., by measurement of code-phased arrival times of four different GPS signals), a GPS receiver device can compute an estimate of the receiver device's position in three dimensions (e.g., altitude, latitude and longitude or X, Y and Z), an estimate of the receiver device's velocity (if the receiver is moving), and a time offset for a clock operating within the receiver device based on satellite clock information in the GPS signals.
Navigation in three dimensions is the primary function of conventional GPS systems and receivers designed for navigation are manufactured by various vendors for use within aircraft, ships, ground vehicles, and for hand carrying by individuals. In addition, the GPS system may be used for positioning purposes, time dissemination, surveying and geographic research (e.g., studies of plate tectonic movement) as well.